EXAMINATION OF PLASTIC PARTICLES IN THE SURFACE WATERS OF THE CARQUINEZ STRAIT, SAN FRANCISCO ESTUARY, CALIFORNIA

This study examines the type and abundance of plastic particles in the surface waters of the Carquinez Strait, San Francisco Estuary, California. The San Francisco Estuary consists of three bays: the San Francisco Bay, east of the Golden Gate Bridge, and San Pablo Bay and Suisun Bay, located in the northern part of the estuary. The Carquinez Strait, a narrow waterway connecting San Pablo Bay and Suisun Bay, experiences significant tidal mixing, as well as large urban and industrial impacts. The aim of this study is to provide insights into the influence of tides on plastic distribution. Previous studies of surface water plastics in the northern San Francisco Estuary are scarce, and the area did not receive the same scientific attention as the San Francisco Bay even though they are both crucial ecosystems of the estuary.

We present here preliminary results based on surface water samples collected along the westernmost part of the Carquinez Strait and easternmost border of the San Pablo Bay using a manta trawl. Samples were obtained during high tide as well as low tide. During sampling the vessel maintained an average speed of 3 knots, and the duration of towing was 15 to 30 minutes. At the time of sampling the sea state ranged from 1 to 2. In the laboratory, each water sample was poured from the cod end onto a 500 μm sieve. The cod end was rinsed over the same sieve to make sure no particles were left behind in the cod end. Sample residues were left air drying for 24 hours. Tweezers were used to pick all the colorful, shiny, and artificial-looking pieces from the residues. To ensure the plastic nature of the particles, each particle was gently crushed. Those staying intact were considered plastic and were preserved for further examination under a dissection microscope. The preliminary results revealed three types of plastic: fragments (~50%), lines (~40%), and thin films (~10%). Samples collected during high tide contain in total about 50% more plastic particles. The preliminary conclusion is that tides exert an influence on the number of plastic particles found near the Carquinez Strait. The final results will increase our understanding of the influence of tides in the distribution of plastic particles across the San Francisco Estuary.